1. Field of Invention
The invention relates to a printer architecture. More particularly, this invention relates to a hyperacuity printer architecture. Specifically, this invention relates to a method and system for driving a printing element in a hyperacuity laser printer.
2. Description of Related Art
According to human visual research, the frequency response or resolution of a printing system need only exceed the resolving power of the human visual system. Such resolving power is known as visual acuity. However, there are human visual considerations that require the placement of edges 10-60 times more accurately than that indicated by frequency resolution considerations. These requirements are based on hyperacuity, or the visual system's ability to differentiate locally misaligned edges to a much greater extent than the inter-receptor spacing of the eye. In this case, it is not the frequency response (resolution) of the visual system that is most important, but the ability to reckon edges with high precision. Therefore, placing edges or transitions in images in both a fast scan direction and a process, or slow scan, direction with precision greater than that of the actual printer resolution is necessary. "Hyperacuity Laser Imager" by Douglas N. Curry, Journal of Electronic Imaging, April, 1993, vol. 2(2), pgs. 138-146, herein incorporated by reference in its entirety, provides a detailed description of the relationship between the human visual system and printer resolution.
Two contrasting techniques have evolved over the last two decades to provide high image quality in laser printing, one based on resolution and the other on phase. High resolution platemakers and prepress printers use spot sizes that are the reciprocal of their binary resolutions to produce excellent image quality. These printers are expensive and slow. However, the resolutions of these printers can approach a pleasing 3,000 to 4,000 dots or spots per inch. Desktop laser printers, on the other hand, are more cost constrained and therefore use lower resolution spot sizes and scan frequencies, such as 600 dots per inch. These printers impart high quality to their images by using phase information from the source image to simulate higher resolution. These printers do not improve true image resolution beyond the physical limit of spot size and scan frequency. Rather, these printers obtain high quality through the precise positioning of edges.
There are several conventional techniques for driving printing elements. The template matching technique provides one or more templates, and looks for particular image portions that match one of the templates. Based on the matched template, an edge position is estimated. This information is then output to render edge information, which is used to drive a print element. The template matching technique is further described in U.S. Pat. No. 5,329,599 to Douglas N. Curry, which is incorporated herein by reference in its entirety.
Another technique for driving a printing element involves postscript decomposers, which use stored image information. A postscript image is rendered or converted to a bytemap image. The rendered bytemapped image is output to the printer to drive the print element.